In the oil & gas industry control valves are used to control pressure, level, temperature and flow. In some cases these control valves operate at choked or throttled conditions, once sufficient pressure drop is created over the control valve. In processing natural gas this pressure reduction over a valve causes the temperature to drop without extracting heat or work from the gas. This so called isenthalpic expansion process is also known as Joule-Thompson (JT) cooling. The valve creating this pressure reduction is called a JT valve. The cooling effect over a JT valve is used to condense a part of the natural gas stream, such that the liquefied fraction can be separated in a vessel. For the majority of these separator vessels the driving force is either inertia or gravity forces or in other words the masses of the liquefied drops determine the efficiency of the separation. Such a Low Temperature Separator preceded by a JT valve is normally referred to as a JT-LTS system.
Even though the prime function of a JT valve is flow rate control, it is often forgotten that the second function is to create a separable liquid phase. In the gas processing industry the mean droplet size resulting from an isenthalpic expansion over a JT valve is unknown, hence the separation efficiency of downstream separators is to a large extent unknown. From time to time gas quality problems do occur due to suboptimal separation efficiency. In those cases it is often the hydrocarbon dew point, which remains too high, which indicates that especially hydrocarbon droplets tend to be too small.
International patent application WO 2004/001260 and U.S. Pat. Nos. 4,384,592 and 4,671,321 disclose throttle valves that are equipped with swirl imparting means that generate vortices in the fluid flux passing through the valve.
The valves known from U.S. Pat. Nos. 4,383,592 and 4,671,321 are provided with perforated sleeves in which the perforations have different orientations relative to a central axis of the sleeve, such that a plurality of vortices are generated in the fluid flux passing through the valve, which vortices may be counter-rotating and serve as noise dampeners.
The valve known from International patent application WO2004/001260 is provided with a valve stem that defines a fluidic vortex chamber with both tangential and non-tangential inlets. If the valve is fully open or nearly fully open fluid flows solely through the tangential inlets, without generating a swirl in the fluid flux. If the valve is nearly closed then fluid flows solely through the non-tangential inlets, thereby generating a vortex and resistance to flow, and suppressing erosive and cavitational wear of the valve mechanism.
U.S. Pat. Nos. 4,055,961 and 4,544,390 and International patent application WO2004083691 disclose throttling valves in which gaseous components are condensed as a result of the Joule Thompson effect.
A problem with the known Joule Thomson and other throttling valves is that the size of the condensed liquid droplets is generally small, such that a mist flow is generated from which the liquid and gaseous phases cannot be easily separated.
In an embodiment of the present invention this problem is solved. A throttling valve in which larger liquid droplets can be formed than in the known throttling valves is provided in some embodiments of the present invention.